The quick and inexpensive provision of prototypes (rapid prototyping) is a task frequently set in recent times. Methods working on the basis of powdery materials in which the desired structures are formed layer-wise by selective melting and solidification are particularly suitable. The methods are also suited for the fabrication of small-scale series.
A method that is especially well suited for the purpose of rapid prototyping or the manufacture of components in small-scale series is selective laser sintering. In this method, plastic powders contained in a chamber are selectively exposed to a laser beam for a short period of time causing the powdery particles hit by the laser beam to melt. The melted particles blend into each other and solidify quickly to form a solid mass. In this method, three-dimensional bodies can be produced in a simple and quick way by repeated exposure of continuously applied powder layers.
Plastic powders made of polyester, polyvinyl chloride, polyacetal, polypropylene, polyethylene, polystyrene, polycarbonate, poly-(N-methylmethacrylamide) (PMMI), polymethylmethacrylate (PMMA) and polyamide or mixtures thereof can be used for selective laser sintering. In practice, mainly powders made of polyamide-12 have been used.
The use of powders made of an aliphatic thermoplastic polyurethane (TPU) for the purpose of selective laser sintering has been known from DE 10 2010 062 875, in which the TPU powder is used for the manufacture of automotive components by laser sintering.
The production of aliphatic thermoplastic polyurethanes is for example described in DE 198 00 287 A1, DE 10 2006 021 734 A1 and DE 10 2008 006 004 B3, which are incorporated herein by reference. In addition, a powder made of thermoplastic polyurethane suitable for use in laser sintering processes is commercially available under the trade name Desmosint™ X 92 A-1 (Bayer Material Science AG).
The TPU powder used so far for the laser sintering process has a high melting temperature of more than 150° C. and a relatively high melting viscosity. Furthermore, the powders are recyclable only to a limited degree. Although the components made of the known TPU powders exhibit good mechanical properties, they may have surface defects such as shrink marks.